Tracking issue for RFC 2235, "Implement Debug, Eq, PartialEq, and Hash for libc structs"

[Centril]

This is a tracking issue for the RFC "Implement Debug, Eq, PartialEq, and Hash for libc structs" (rust-lang/rfcs#2235).

Steps:

• Implement the RFC (cc @rust-lang/libs @Susurrus)
• Stabilization PR (see instructions on forge)

Unresolved questions:

• Is it possible to just add #[derive(Debug, Eq, Hash, PartialEq)] since the Copy and Clone traits are directly implemented and not derived?

[Susurrus]

A problem that came up when implementing this is for implementing Hash for types that have floats or doubles in them. For the fpreg_t struct I did the following:

impl std::hash::Hash for fpreg_t {
    fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
        self.d.to_bits().hash(state);
    }
}

We should decide if we want to handle this: avoid it entirely for types that have floats or doubles, implement them like I did above, or sort out a "better" way to deal with hashing them.

[gnzlbg]

Many types still don't implement all of the traits, e.g., grep on libc for missing_debug_implementations, for example.

• Some types can't easily derive(Debug) because they are repr(packed).
• Some types can't easily derive most of the traits because they contain arrays with more than 32 elements.

[jonas-schievink]

@Susurrus is this fully implemented now? rust-lang/libc#1271 seems to indicate so.

[gnzlbg]

It’s mostly implemented, but there is still the unresolved questions about enforcing requiring this and also about whether to enable this by default.

…

On Sun 9. Jun 2019 at 15:42, Jonas Schievink ***@***.***> wrote: @Susurrus <https://github.com/Susurrus> is this fully implemented now? rust-lang/libc#1271 <rust-lang/libc#1271> seems to indicate so. — You are receiving this because you commented. Reply to this email directly, view it on GitHub <#57715?email_source=notifications&email_token=AAG43JSNSPUYYNUXYYFKMRDPZUCDVA5CNFSM4GQ3LWSKYY3PNVWWK3TUL52HS4DFVREXG43VMVBW63LNMVXHJKTDN5WW2ZLOORPWSZGODXIKMQA#issuecomment-500213312>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAG43JXM6TBSJ2TRE3DL7UDPZUCDVANCNFSM4GQ3LWSA> .

[joshtriplett]

This is mostly implemented, and to the extent it isn't, it's a libc issue rather than a rust-lang/rust issue. Closing; please feel free to open an issue on libc for any remaining aspects of it.